This invention relates to a composition and process for processing radioactive waste materials to render them suitable for shipment and/or storage. Radioactive waste materials, especially those resulting from the processing of uranium and plutonium, are particularly dangerous to transport to sites for final disposition, such as long-term storage or further processing. Such waste encompasses a wide range of material, and may include piping, building materials, machinery and equipment, furniture, weapons casings and the like.
Radioactive waste, especially from the processing of uranium and plutonium, is usually buried for its final disposition. The current state of technology includes the steps of filling all of the interstitial spaces in the radioactive material with cement, and then micro-encapsulating the material with more cement. There are several shortcomings to this method. First, the resultant encapsulating material is very heavy. Cement has a typical density about 120 lbs/ft3, so it would not be unusual to have a large piece of contaminated equipment weigh in excess of 100,000 lbs. This necessitates the use of expensive, heavy equipment to move these structures. Second, the pouring of cement in situ over the encapsulated material (i.e. in the landfill) is an extraordinarily inefficient use of space. A large amount of cement is spilled over the sides of the material due to the inexact nature of pouring cement. This causes much more landfill space to be used than would be the case with a more focused process. Third, cement is well known to crack when exposed to tensile stress, temperature extremes, or when non-optimal water/cement ratios are used. When cracking in these monolithic structures occurs, there is a greater risk that radioactive waste will migrate from the structure into an uncontrolled environment.
The use of polyurethanes for the purpose of encapsulation of radioactive materials is known in the prior art. The known prior art describes the use of one of several types of cement/mortar, sand, filler, or other additives to the polyurethane to either create a high density monolithic block, or as an aid for radiation attenuation. The novelty of the present invention resides in the lack of solid fillers or cement/mortar, as well as the optional inclusion of an elastomeric coating to encapsulate and protect the radioactive material from possible damage in transport.
UK Patent No. GB2047946 to Pordes et al. discloses the encapsulation of radioactive waste material, particularly wet ion exchange resin, by dispersing the waste in an aqueous emulsion of an organic polyol, a polyisocyanate and an hydraulic cement, and allowing the emulsion to react and form a monolithic block.
U.S. Pat. No. 7,250,119 to Sayala discloses the use of naturally occurring minerals in synergistic combination with formulated modified cement grout matrix, polymer modified asphaltene and maltene grout matrix, and polymer modified polyurethane foam grout matrix to provide a neutron and gamma radiation shielding product.
U.S. Pat. No. 4,100,860 to Gablin et al. discloses a shipping container overpack for transportation of radioactive materials, and includes a leakproof receptacle for containing and protecting the material against accidental release. The receptacle has spaced inner and outer shells into which polyurethane foam is poured to create a stress skin structure.
U.S. Pat. No. 4,486,512 to Tozawa et al. discloses a waste sealing container constructed by depositing a foundation of zinc over a steel base, then coating an organic synthetic resin paint containing a metal phosphate over the foundation coating, and thereafter coating an acryl resin, epoxy resin, and/or polyurethane paint.
The above-described processes and resulting structures retain many of the disadvantages of the prior art, and thus a more cost-effective, efficient and safe means of processing radioactive waste for shipping and storage is needed.